30 ] The Classificatio7i of Lower Organisms 



Order Schizophyceae Schenck in Strasburger et al. Lehrb. Bot. 1894. 



Class Schizophyceae Engler in Engler and Prantl Nat. Pflanzenfam. I Teil, Abt. 

 la: iii (1900). 



Class Archiplastideae Bessey in Univ. Nebraska Studies 7: 279 (1907). 



Class Cyanophyceae Schaffner in Ohio Naturalist 9: 446 (1909). 



Class Myxophyceae G. M. Smith (1918). 



Subclass Myxophyceae Setchell and Gardner in Univ. California Publ. Bot. 8, 

 part 1: 3 (1919). 



Cyanophyta Steinke ( 193 1 ) . 



Stamm Cyanophyta Pascher in Beih. Bot. Centralbl. 48, Abt. 2: 330 (1931). 



Mychota most of which live by phytosynthesis of primitive or typical character, 

 many of them, and most of the saprophytic and chemosynthetic organisms included 

 with them, being of the form of sheathed filaments. 



This is primarily the group of the blue-green algae. Blue-green algae are familiar 

 things as forming dark scums in water and on wet surfaces. Rabenhorst (1863) ap- 

 pears first to have recognized them as a group definitely distinct from green algae; 

 he named most of the recognized families. Revisions by Thuret (1875), Bomet and 

 Flahault (1886-1888), and Gomont (1892) failed to provide a satisfactory system 

 of the group; Kirchner's revision (in Engler and Prantl, 1898) is the accepted system. 



One of the important contributions of Cohn was his suggestion that the bacteria 

 and blue-green algae belong together. He emphasized this view by mingling the 

 genera of the two groups in two new groups, "tribes," named in effect slime-formers 

 and thread-formers (1875). In this he went too far; but some of the arrangements 

 which he suggested appear natural. Beggiatoa, the type of order Thiobacteria of 

 Migula, appears to be a variant of the common blue-green alga Oscillatoria, differing 

 from it in living by chemosynthesis. Most of the so-called iron bacteria, family 

 Chlamydobacteriaceae of Migula, fall readily into scattered places among the blue- 

 green algae. Only the genus Sphaerotilus remains at loose ends. It is credibly reported 

 to produce cells swimming by means of flagella; no proper blue-green algae do this. 



A variety of purple bacteria — bacteria, that is, which contain a red pigment — 

 have been discovered from time to time. Engelmarm (1888) observed that they swim 

 toward the light, and convinced himself that they live by photosynthesis. Van Niel 

 confirmed this, and showed that photosynthesis is in this group of a peculiar character; 

 it requires the presence of reducing agents and does not release oxygen. This type of 

 photosynthesis appears, in fact, to represent a stage of the evolution of typical photo- 

 synthesis; the group in which it occurs appears to represent the ancestry of the 

 typical blue-green algae. The poorly known green bacteria appear to belong with 

 the purple bacteria. 



Various members of this class have been proved capable of fixing nitrogen (Sisler 

 and ZoBell, 1951; Williams and Burris, 1952). 



Four orders may be distinguished: 



1. Possessing a red ("purple") intracellular 

 pigment, or a green pigment not masked by 

 others Order 1 . Rhodobacteria. 



l.With green pigment masked by others, or 

 colorless. 



2. Producing cells with flagella; non-pig- 

 mented sheathed filaments not accumu- 

 lating ferrugineous matter Order 2. Sphaerottlalea. 



